PROJECT SUMMARY Schizophrenia is a debilitating lifelong psychiatric disorder with a worldwide prevalence of 1%. It is characterized by positive symptoms (delusions, hallucinations, disorganized thinking), negative symptoms (flattened affect, anhedonia, paucity of speech) and cognitive symptoms (defects in executive function, attention, and working memory (WM)). While the positive symptoms can be effectively managed with antipsychotic drugs, there are no treatments for the negative and cognitive symptoms. Recent PET imaging of schizophrenic patients has confirmed that there is a cortical dopamine (DA) deficit following a challenge with the DA releasing drug amphetamine (AMPH). This deficit in cortical DA has long been thought to play a critical role in the pathology of the negative and cognitive symptoms of schizophrenia, including the deficit in WM. Due to a lack of tools with which to study neurotransmission with single synapse resolution in vivo, the nature of this deficit has yet to be determined. In order to study DA neurotransmission in vivo with single synapse resolution, we have optimized a novel tool for in vivo multiphoton imaging of mice. Fluorescent false neurotransmitters (FFNs) are fluorescent substrates for the DA transporter (DAT), the norepinephrine transporter (NET), and the vesicular monoamine transporter (VMAT), that are taken up into the presynaptic boutons of axons where they are subsequently loaded into presynaptic vesicles. FFNs have previously been used in acute brain slice experiments to allow determination of the kinetics of synaptic release, however, their use in vivo is an unpublished application. We have used FFNs to image catecholamine neurotransmission in the cortex in vivo. For this project, we will utilize multiphoton imaging in vivo of FFNs and GCaMP6f, to record DA release from presynaptic mesocortical terminals in the medial prefrontal cortex of WT and schizophrenia model mice both during AMPH induced electrically evoked, and spontaneous release and during a task of WM. This proposal implements a novel method to examine DA release in vivo in WT and two mouse models of schizophrenia to provide the first measurement of in vivo kinetics of DA during both AMPH induced release and a task of WM. Elucidating the mechanism underlying DA deficits in schizophrenia mouse models may provide key translational information for the changes that occur in schizophrenic patients and may reveal new targets to aid future therapeutic strategies.